An apparatus for controlling a motor using an inverter operates a motor by measuring a flux and using the measured flux or by detecting or estimating a position or a speed of a rotor of the motor and using the detected or estimated position or speed. Generally, a method of measuring the position and speed of the motor is classified into a method using an analog sensor and a method using a digital sensor. The analog method based measurement apparatus is a synchro, a resolver, a taco-generator, or the like and is configured to measure a position based on a displacement amount of the rotor converted into an analog amount.
Further, in a blush-less DC (BLDC) motor, the position of the rotor is required to be determined to implement functions of a commutator and a brush as a power semiconductor switch. The rotor is configured as a permanent magnet, and therefore the position of the rotor is searched using a flux detection sensor such as a hall element. In a method using the resolver, the resolver generally outputs a sensed electrical angle of the motor to a resolver digital converter (RDC) as a signal form, in which the RDC detects the position of the rotor of the motor and outputs the detected signal to a controller. However, when the temperature of the inverter rises, a magnitude of the signal applied to the resolver is amplified. In particular, a magnitude of a signal output from the resolver is also increased. When the signal from the resolver is amplified to a fixed gain, the output signal may be excessive or insufficient, such that a signal to noise ratio may be reduced.